The present invention relates to a laser system for the treatment of body tissue on an inner circumferential tissue surface and to a related method.
Various laser wavelengths, which are highly absorbed in water, such as Er:YAG (2.94 μm wavelength), Er,Cr:YSGG (2.73 μm wavelength), CO2 (8-11 μm wavelength) have been advocated as possible and promising alternatives to conventional instruments in different medical and surgical disciplines. Due to their characteristic absorption maxima in water which is an important constituent of body tissues, they are considered to be suitable not only for the treatment of soft tissue structures but also for ablating mineralized hard tissues. Contact-free laser ablation offers the opportunity of cutting bone and other hard tissue without friction that may cause additional thermal and mechanical trauma. Consequently, the risk of cell death and delayed healing may be minimized. Furthermore, in contrast to conventional procedures, no tissue particles debris is left on the tissue surface leading to a smear layer on the treated surface. This is due to the laser tissue ablation mechanism. Absorption and the following transformation of laser irradiation into heat result in a rapid phase change which, in turn, creates internal pressures, causing micro-fracturing and micro-explosive removal of the mineral phase of the hard tissues. Besides, during the laser ablation of the tissue, the vaporization of water leads to a fast removal of the tissue layers. The result is an extremely clean and micro-structured tissue surface without thermal damage and smear layer, resulting in reduced inflammatory response and accelerated tissue regeneration and attachment. This is, for example, important in implantology where faster attachment of the bone to the inserted implants is crucial for faster patient recovery time.
Nevertheless, drawbacks of hard tissue laser surgery such as a considerable amount of time needed, lack of depth control, and highly sophisticated handling requirements are still formidable. An advantage of mechanical tools such as drills and saws is that the surgeon has a very good tactile contact with the treated tissue providing feedback to the surgeon regarding the speed of the procedure and the depth of the drilled hole or cut. For this reason, laser bone cutting is still assessed to be inferior to many conventional as well as other methods, such as piezoelectric osteotomy. In particular, when creating a hole in hard body tissue like bone material, mechanical tools are commonly still preferred. This preference however leaves unanswered the question of how to handle the aforementioned issues like e.g. residual smear layers on the inner circumferential body tissue surface of said hole. The treatment results of the inner circumferential body tissue surface by mechanical means are unsatisfactory. The same applies to soft tissue treatment on inner circumferential body surfaces as performed e.g. in vaginal or anal treatments. It is therefore desirable to develop means to treat circumferential body tissue surfaces with a laser.
One possible solution for treating circumferential body tissue surfaces involves a laser system comprising of a laser source for the generation of a laser beam and a handpiece with a special reflection mirror treatment head, as disclosed in WO 2012/037954 A1. The laser system comprises a laser source for generating a laser beam and a handpiece with a treatment head. The treatment head extends along a longitudinal axis and is adapted in a manner such that the longitudinal axis of the treatment head during operation is at least approximately parallel to the inner circumferential tissue surface. During operation, the laser beam enters the treatment head in the direction of the longitudinal axis. A reflection mirror with a conical shape is disposed in the treatment head and guides the laser beam radially outwards out of the treatment head onto the inner circumferential tissue surface. Movable deflection means for the laser beam are provided to scan the inner circumferential tissue surface within a treatment area at least in a circumferential direction. One drawback of this solution is that the treatment head must consist of mechanical means for holding the conical reflection mirror in the proper position, making the design and manufacture of such treatment head relatively difficult. Another drawback of this solution is that the reflected beam gets spread out not only in the transverse direction, due to the circular shape of the treatment head, but also in the longitudinal direction due to the varying radius of the cone in the longitudinal direction.
Another option for treating circumferential body tissue surfaces with a laser is to use a fiber tip with a conical end. Using this solution, the fiber tip is positioned at least approximately parallel to the inner circumferential tissue surface. The laser beam is guided within the fiber tip dimensions in such a manner that the beam extends substantially over the whole cross section of the fiber tip. Because of the conical end of the tip, the beam, before exiting the tip, is at least partially reflected on the conical tip surface, resulting in the exiting beam being at least partially guided radially outwards out of the fiber tip and unto the inner cavity circumferential tissue surface. This solution is mechanically less complex than the solution with the reflection mirror treatment head. However, it is unsatisfactory when high power densities are required to treat or modify the tissue. Since the energy of the beam is distributed over the whole circumference of the body cavity, the resulting laser power density (in W/cm2) is significantly reduced. For this reason, the conical fiber tip technique is unsuitable for treating larger diameter cavities, where the reduction in laser power density is most pronounced. Another drawback of this solution is that the body tissue is being treated indiscriminately over the whole circumference of the cavity. In some medical procedures, it is desirable that certain areas of the cavity remain untreated, or treated with a different energy. For example, in gynecological treatments, it may be desirable to avoid a laser irradiation of the urethra. A third drawback of this solution is that the laser beam impacts also on the sharp apex of the conical surface. It is technologically challenging, if not impossible, to manufacture a perfect apex. In addition, at high laser intensities, and with continued use, it is this apex that becomes damaged first. For this reason, the part of the beam which impinges on the apex becomes at least partially transmitted also in the forward (longitudinal) direction, possibly damaging the tissue at the bottom of the treated cavity.
The invention has the object to provide an improved laser system which allows treating circumferential body tissue surfaces of large diameters.